Extend supported Python versions to 3.10, drop 3.3 from CI

Python 3.3 testing has not worked for a long time, but was still
taken into account in the .travis.yml. See #69.

.travis.yml

@@ -3,11 +3,12 @@ python:
   - "2.7"
   - "3.4"
   - "3.6"
+  - "3.10"
 branches:
   except:
     - piptools-ignore-patch
 install:
-  - "python -c 'import sys; sys.exit(0 if (3, 3) <= sys.version_info < (3, 4) else 1)' && pip install pip==10.0.1 setuptools==39.2 wheel==0.29.0 || pip install -U setuptools pip wheel"
+  - "pip install -U setuptools pip wheel"
   - "pip install cram"
   - "pip install ."
 script:

setup.py

@@ -40,21 +40,16 @@
         # 'Development Status :: 7 - Inactive',
         'Programming Language :: Python',
         'Programming Language :: Python :: 2',
-        # 'Programming Language :: Python :: 2.3',
-        # 'Programming Language :: Python :: 2.4',
-        # 'Programming Language :: Python :: 2.5',
-        # 'Programming Language :: Python :: 2.6',
         'Programming Language :: Python :: 2.7',
         'Programming Language :: Python :: 3',
-        # 'Programming Language :: Python :: 3.0',
-        # 'Programming Language :: Python :: 3.1',
-        # 'Programming Language :: Python :: 3.2',
         'Programming Language :: Python :: 3.3',
         'Programming Language :: Python :: 3.4',
         'Programming Language :: Python :: 3.5',
         'Programming Language :: Python :: 3.6',
         'Programming Language :: Python :: 3.7',
         'Programming Language :: Python :: 3.8',
+        'Programming Language :: Python :: 3.9',
+        'Programming Language :: Python :: 3.10',
         'Intended Audience :: Developers',
         'Intended Audience :: System Administrators',
         'License :: OSI Approved :: BSD License',

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = py27,py34,py36
+envlist = py27,py34,py36,py310
 
 [testenv]
 deps=cram